Answer:
Cancer (or malignant tumor) is the name given to a set of more than 100 diseases that have disordered cell growth in common. Dividing rapidly, these cells clump together to form tumors that invade tissues and can invade neighboring and even distant organs of the tumor (metastases). Cancer is caused by mutations, which are changes in the genetic structure (DNA) of cells. Each healthy cell has instructions on how to grow and divide. In the presence of any error in these instructions (mutation), a diseased cell may arise which, upon proliferation, will cause cancer. Cancer can arise anywhere in the body. However, some organs are more affected than others; and each organ, in turn, may be affected by different or more aggressive tumor types.
Cancer has no single cause. There are several external causes (present in the environment) and internal causes (such as hormones, immune conditions and genetic mutations). Factors can interact in many ways, triggering the onset of cancer.
